This disclosure relates generally to processes for the formation of silicon-containing overcoat layers, and to the use of such silicon-containing overcoat layers in electrophotographic imaging members. In particular, this disclosure provides a method for producing silicon-containing overcoat layers by sol-gel processes including disilanol compounds.
In electrophotography, an electrophotographic substrate containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging a surface of the substrate. The substrate is then exposed to a pattern of activating electromagnetic radiation, such as, for example, light. The light or other electromagnetic radiation selectively dissipates the charge in illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in non-illuminated areas of the photoconductive insulating layer. This electrostatic latent image is then developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image is then transferred from the electrophotographic substrate to a necessary member, such as, for example, an intermediate-transfer member or a print substrate, such as paper. This image-developing process can be repeated as many times as necessary with reusable photoconductive insulating layers.
Image-forming apparatus such as copiers, printers and facsimiles, including electrophotographic systems for charging, exposure, development, transfer, etc., using electrophotographic photoreceptors have been widely employed. In such image-forming apparatus, there are ever-increasing demands for improving the speed of the image-forming processes, improving image quality, miniaturizing and prolonging the life of the apparatus, reducing production and running costs, etc. Further, with recent advances in computers and communication technology, digital systems and color-image output systems have been applied also to image-forming apparatus.
Electrophotographic imaging members (i.e. photoreceptors) are well known. Photoreceptors having either a flexible belt or a rigid drum configuration are commonly used in electrophotographic processes. Photoreceptors may comprise a photoconductive layer including a single layer or composite layers. These photoreceptors take many different forms. For example, layered photoresponsive imaging members are known in the art. U.S. Pat. No. 4,265,990 to Stolka et al., which is incorporated herein by reference in its entirety, describes a layered photoreceptor having separate photogenerating and charge-transport layers. The photogenerating layer disclosed in the 990 patent is capable of photogenerating holes and injecting the photogenerated holes into the charge-transport layer. Thus, in the photoreceptors of the 990 patent, the photogenerating material generates electrons and holes when subjected to light.
More advanced photoconductive photoreceptors containing highly specialized component layers are also known. For example, multi-layered photoreceptors may include one or more of a substrate, an undercoat layer, an intermediate layer, an optional hole- or charge-blocking layer, a charge-generating layer (including a photogenerating material in a binder) over an undercoating layer and/or a blocking layer, and a charge-transport layer (including a charge-transport material in a binder). Additional layers, such as one or more overcoat layer or layers, may be included as well.
In view of such a background, improvement in electrophotographic properties and durability, miniaturization, reduction in cost, etc., in photoreceptors have been studied, and photoreceptors using various materials have been proposed.
For example, JP-A-63-065449 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), discloses photoreceptors in which fine silicone particles are added to a photosensitive layer, and also discloses that such addition of the fine silicone particles imparts lubricity to a surface of the photoreceptor.
Further, in forming a photosensitive layer, a method has been proposed in which a charge-transfer substance is dispersed in a binder polymer or a polymer precursor thereof, and then the binder polymer or the polymer precursor thereof is cured. JP-B-05-047104 (the term “JP-B” as used herein means an “examined Japanese patent publication”) and JP-B-60-022347, disclose photoreceptors using silicone materials as the binder polymers or the polymer precursors thereof.
Furthermore, in order to improve mechanical strength of the photoreceptor, a protective layer is formed on the surface of the photosensitive layer in some cases. Often, a cross-linkable resin is used as a material for the protective layer. However, protective layers formed by cross-linkable resin act as insulating layers, which impair the photoelectric characteristics of the photoreceptor. For this reason, a method of dispersing a fine conductive metal oxide powder, as disclosed in JP-A-57-128344, or a charge-transfer substance, as disclosed in JP-A-04-015659, in the protective layer and a method of reacting a charge-transfer substance having a reactive functional group with a thermoplastic resin to form the protective layer have been proposed.
However, even the above-mentioned conventional photoreceptors are not necessarily sufficient in electrophotographic characteristics and durability, particularly when used in combination with a charger of the contact-charging system (contact charger) or a cleaning apparatus, such as a cleaning blade.
Further, when the photoreceptor is used in combination with the contact charger and a toner obtained by chemical polymerization (polymerization toner), image quality may be deteriorated due to a surface of the photoreceptor being stained with a discharge product produced in contact charging or the polymerization toner remaining after a transfer step. Still further, the use of a cleaning blade to remove discharge product or remaining toner from the surface of the photoreceptor involves friction and abrasion between the surface of the photoreceptor and the cleaning blade, which tends to damage the surface of the photoreceptor, break the cleaning blade or turn up the cleaning blade.
The use of silicon-containing compounds in photoreceptor layers, including in photosensitive and protective layers, has been shown to increase the mechanical lifetime of photoreceptors, under charging conditions and scorotron-charging conditions. For example, U.S. Patent Application Publication No. 2004/0086794 to Yamada et al., which is incorporated herein by reference in its entirety, discloses a photoreceptor having improved mechanical strength and stain resistance.
Photoreceptors having low wear rates, such as those described in U.S. Patent Application Publication No. 2004/0086794, also have low refresh rates. Low wear and refresh rates are a primary cause of image-deletion errors, particularly under conditions of high humidity and high temperature. U.S. Pat. No. 6,730,448 to Yoshino et al., which is incorporated herein by reference in its entirety, addresses this issue in its disclosure of photoreceptors having some improvement in image quality, fixing ability, even in an environment of high heat and humidity.
It has been determined that, in photoreceptors, deletion of a developed image can degrade the top-most surface of the photoreceptor. This deletion can occur when the photoreceptor is exposed to environmental contaminants, such as those typically found around the charging device of a xerographic engine. The image deletion can increase under conditions of high heat and/or high humidity.
In typical photoreceptors, where the outermost surface comprises a solid-state solution of a hole-transporting arylamine compound in a polymeric binder material, image-deletion can occur when the environmental contaminants around the charging device react with hole-transporting arylamine compounds to form highly conductive species.
However, in photoreceptors in which the outermost layer is a siloxane-organic hybrid material containing a hole-transporting arylamine moiety, image deletion can occur when the environmental contaminants around the charging device in the xerographic engine interact with the siloxane component of the siloxane-organic hybrid material. A chemical reaction by which residual alkoxides of the siloxane components hydrolyze to form highly polar silanol moieties can result from this interaction. These highly polar silanols, which reside on the outermost photoreceptor surface and both attract and retain environmental contaminants formed by the charging device, can cause highly conductive zones to form on the photoreceptor surface. In the presence of high heat and/or high humidity, these highly conductive zones can manifest as a deletion of the developed image.
Thus, the above-mentioned conventional photoreceptors are not necessarily sufficient in electrophotographic characteristics and durability, particularly when used in high-heat and/or high-humidity environments.
Thus, there still remains a need for photoreceptors having high mechanical strength and improved electrophotographic characteristics and improved image-deletion characteristics even under conditions of high temperature and high humidity.